Ok , here are the codes that came up . 15,21,22,23,44,45, and 51 . He wanted to replace the ECU and the PROM .

 

im having same issue, any ideas yet?
and did you properly change the gaskets on the tstats

 

The problem is the OEM routing of your heater core lines, they go back to the radiator instead of the water pump (see attachment #1 previous post, look below the radiator cap).

When you rev your engine the water pump circulates a ton of coolant and in doing so it sucks a bunch of cold fluid in from the radiator, causing instant temperature drop in the heads and intake. Not as dramatic once you have been running at temperature for a while, but that can take forever in the winter

The fix is to get a water pump hose barb nipple (napa,etc..) and then splice/plug the heater core return line where it goes into your radiator. Caveat is your engine will sometimes run a bit warmer than T-stat because of the restriction at the T-stat, but it's never been a serious problem for me and I run a vortec-tbi with custom tune that sometimes yields very high EGTs during long hill climbs. Maybe 210*-215* max in summer time (measured by CTS using ALDL cable & tunerpro)


BTW, Junkyard tbi ECM's are DIRT CHEAP and are usually fine (99%). Any 7747 from '87-'92 in a half ton chevy with your powertrain will work (350/700r4 was very common). Everybody should have a spare or 2...